Ceiling cabin light question...

I have a 1968 Cherokee 180D. Both the ceiling mounted white cabin light and red light are out. I can not figure how to get the cover off the white light. I've tried twisting it to see if it was 'tab' locked with no luck. It doesn't seem to unscrew. I removed the ceiling panel, but that only gave access to the top of the bulb receptacle for the white light with screw tips showing that obviously screwed in from under the light cover. The red light wasn't any easier to decipher.

Any assistance would be GREATLY appreciated.

Quincy...

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I'm a little confused. If you were able to remove the cover--as shown in the picture you attached--didn't that give you access to the bulbs?? I seem to remember that the bulbs are replaced by push, one-eighth turn and release.
What am I missing??